Key switches of a variety of styles are in widespread use to enable manual entry of alphanumeric information or other instructions in data-processing equipment, typewriters and teletypes, calculators, and similar equipment. A number of individual key switches, typically of a single-pole single-throw type, are usually clustered together in a common frame to form a keyboard for data entry. Each switch is provided with a key cap which displays a symbol representing the switch function, and which is depressed by an operator to actuate the switch.
Key switches are often the only moving parts in a data-entry system, and it is important that these components be sufficiently rugged to withstand heavy service over a long operating life. It is equally important for the switch to have an actuating stroke which is comfortable for the operator, and which provides a tactile sensing of switch actuation as the key cap is depressed. The switch should also have a hysteresis characteristic in the actuating stroke to avoid switch jitter or multiple actuations if the operator "teases" the switch at the operating point of the actuating stroke. These functions are described in greater detail in U.S. Pat. No. 3,777,090, the disclosure of which is incorporated herein by reference.
The present invention is a new style of key switch which uses relatively few component parts for reduced assembly complexity and manufacturing cost, and which has an overall geometry enabling a number of switches to be grouped together in a compact keyboard. The switch provides a mechanical advantage in that the actuating force sensed by the operator is lower than the spring force urging the contacts together when the switch is closed. The switch also incorporates the desired characteristics of tactile sensing of the actuation point, and hysteresis to prevent "teasing" of the switch closure.